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KW - N-Heterocyclic carbene (NHC) ligands

N-heterocyclic carbenes in catalytic organic synthesis

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N-Heterocyclic Carbenes in Catalytic Organic Synthesis

References:
1) Polymer-Supported, Carbon Dioxide-Protected N-Heterocyclic Carbenes: Synthesis and Application in Organo- and Organometallic Catalysis, G. M. Pawar, M. R. Buchmeiser, Adv. Synth. Catal., 352 (5) 917-928 (2010)
2) Ring-Opening Metathesis Polymerization-Derived, Polymer-Bound Cu-Catalysts for Click-Chemistry and Hydrosilylation Reactions Under Micellar Conditions, G. Pawar, B., Bantu, J. Weckesser, S. Blechert, K. Wurst, M. R. Buchmeiser, Dalton Trans., 9043-9051 (2009)
3) Alternating Ring-Opening Metathesis Copolymerization by Grubbs-Type Initiators Based On Unsymmetrical N-Heterocyclic Carbenes, M. Lichtenheldt, D. Wang, K. Vehlow, I. Reinhardt, C. Kühnel, U. Decker, S. Blechert, M. R. Buchmeiser, Chem. Eur. J., 15, 9451-9457 (2009)
4) Ru-Alkylidene Metathesis Catalysts Based on 1,3-Dimesityl-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidenes: Synthesis, Structure, and Activity, P. S. Kumar, K. Wurst, M. R. Buchmeiser, Organometallics, 28, 1785-1790 (2009)
5) Polymer-Supported Well-Defined Metathesis Catalysts, M. R. Buchmeiser, Chem. Rev., 109 (2), 303-321 (2009)
6) CO2- and SnII-Adducts of N-Heterocyclic Carbenes as Delayed Action Catalysts For Polyurethane Synthesis, B. Bantu, G. M. Pawar, U. Decker, Klaus Wurst, A. M. Schmidt, M. R. Buchmeiser, Chem. Eur. J., 15, 3103-3109 (2009)
7) Alternating Copolymerizations Using a Grubbs-Type Initiator Based on an Unsymmetrical, Chiral N-Heterocyclic Carbene, K. Velow, D. Wang, S. Blechert, M. R. Buchmeiser, Angew. Chem., 120, 2655-2658 (2008); Angew. Chem. Int. Ed., 47, 2615-2618 (2008)

12/07/2014 · N-Heterocyclic Carbenes: Effective Tools for Organometallic ..

"Science of Synthesis: N-Heterocyclic Carbenes in Catalytic Organic Synthesis" presents the most commonly used and significant metal- or non-metal-catalyzed reactions for modern organic synthesis.

N-heterocyclic Carbenes - Chemistry LibreTexts

N-Heterocyclic carbene based catalysts are now widely applied in the area of synthesis of both natural products and therapeutic agents.

Several different projects entail the use of tailored N-heterocyclic carbenes (NHCs), e.g., for use in polymerization reactions. Taking advantage of their high basicity and pronounced nucleophilic character, NHCs can also be protected by different means, e.g., by the addition of CO2 or by suitable transition metal ions. The thus prepared systems then serve as latent catalysts, e.g., for the synthesis of poly(urethane)s via reaction injection molding of one-component systems. Complementary, the novel NHCs are used for the synthesis of the corresponding transition metal-NHC complexes, which serve as excellent catalysts for C-C coupling reactions including Heck-, Suzuki-, Sonohashira-Hagihara, carbonyl-hydrocyanation, -arylation and hydrosilylations, olefin hydrosilylation reactions as well as various metathesis-based reactions. Finally, suitable immobilization technologies allow for generating immobilized catalysts for continuous flow applications.

This chapter describes the important classes of nickel complexes of N-Heterocyclic carbene (NHC), with attention to the available oxidation states of nickel, the structural characteristics of NHC ligands most widely employed with nickel, and the stabilizing ligands often found in nickel complexes that facilitate generation and handling of the reactive nickel-NHC motif. It also describes the classes of catalytic processes that have been most significantly impacted by the unique characteristics of nickel- NHC complexes. Some of the catalytic processes discussed are cross-coupling reactions, oxidation/reduction reactions, hydrosilylation, and isomerization reactions. Significant developments in the generation of new classes of nickel-NHC catalysts and in the discovery of unprecedented classes of catalytic transformations will undoubtedly continue to arise from this rapidly evolving field.

N-Heterocyclic Carbenes | Sigma-Aldrich

This review article highlights the application of NHC-catalyzed reactions including enantioselective reactions to the heterocyclic synthesis.

Inspired by the tautomeric relationship of imidazole and N-heterocyclic carbenes, we have been intrigued about the implications of such carbenes in metalloenzymes. Enzymes are the machinery of all biological transformations, and provide inspiration for designing artificial catalysts. New insights into the mode of action of enzymes is therefore instrumental for developing more competent synthetic catalysts as well as for better understanding natural systems. In collaboration with F. Paradisi (U Nottingham), we have begun to explore carbene binding to metalloenzymes. We have been focusing on blue copper proteins such as azurin and specific mutants of azurin to investigate the possibility of carbene bonding to the copper center, and to evaluate the effect that such bonding entails. While azurin is predominantly involved in electron transfer processes through reversible copper(II) reduction and oxidation, other blue copper proteins are catalytically active in redox transformations of substrates. Hence, these enzymes provide an attractive probe to explore the relevance of carbene bonding on the catalytic performance of the enzyme.

Description :In less than 20 years N-heterocyclic carbenes (NHCs) have become well-established ancillary ligands for the preparation of transition metal-based catalysts. This is mainly due to the fact that NHCs te...

Publications – N-Heterocyclic Carbenes
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  • Science of Synthesis: N-Heterocyclic Carbenes in …

    The figure below depicts only one of two possible n → 2pz interactions in free N-heterocyclic carbenes

  • The field of N-heterocyclic carbenes, ..

    N-Heterocyclic Carbenes

  • 2002-2012 – N-Heterocyclic Carbenes

    Complexes with a Phenylpropene-derived π/σ-Chelator and N-heterocyclic Carbenes" ..

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Chiral N-Heterocyclic Carbenes - Organic chemistry

AB - This chapter describes the important classes of nickel complexes of N-Heterocyclic carbene (NHC), with attention to the available oxidation states of nickel, the structural characteristics of NHC ligands most widely employed with nickel, and the stabilizing ligands often found in nickel complexes that facilitate generation and handling of the reactive nickel-NHC motif. It also describes the classes of catalytic processes that have been most significantly impacted by the unique characteristics of nickel- NHC complexes. Some of the catalytic processes discussed are cross-coupling reactions, oxidation/reduction reactions, hydrosilylation, and isomerization reactions. Significant developments in the generation of new classes of nickel-NHC catalysts and in the discovery of unprecedented classes of catalytic transformations will undoubtedly continue to arise from this rapidly evolving field.

N-Heterocyclic Carbenes - Yumpu

We are fascinated by the diversity of effects that ligands can have to instigate new properties in transition metal complexes and we are therefore strongly interested in designing and developing new ligands that impart specific properties to the metal center. One of these ligands are triazolylidenes, a mesoionic carbene that we discovered in 2008. This ligand offers various opportunities for catalysis, including strong electron donor properties, a high synthetic flexibility that allows for a wide variety of functional and chelating groups to be incorporated, and a high polarity, which imparts solubility in water and other polar media. We have obtained evidence in a variety of catalytic reactions like nickel-catalysed hydrosilylation, ruthenium-catalyzed alcohol dehydrogenation, or iridium-catalyzed water oxidation, that the triazolylidene ligand scaffold is controlling the reactivity of the coordinated metal center. Because of the synthetic versatility and the easy accessibility of the ligand, tailoring of the ligand properties is straightforward and we have disclosed improved catalytic activity by ligand tuning. More recently, we have discovered a straightforward approach to functionalize the ligand on the complex as opposed to the more traditional approach of preparing a functional ligand and only then install the metal center. This approach gives rapid access to a large diversity of functionalized ligands in a very last step, and to ligand scaffolds that are not accessible by traditional routes.

N-Heterocyclic Carbenes (RSC Publishing)

Description :Over the last fifteen years, N-heterocyclic carbenes (NHCs) have mostly been used as ancillary ligands for the preparation of transition metal-based catalysts. Compared to phosphorus-containing ligand...

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